hvac,air movement, static pressure,ESP

[Yunushumayun]

I know that for a non-ducted exhaust system, usually the SP ranges between .05" to .20"

Do we have any standard showing the above values to prove to our client, someone please share the reference

 

[EnergyProfessional]

I guess the reference would be the source who gave you that knowledge.

I never heard of that "rule of thumb", but assume this is an assumption of the pressuredrop required to move the air in the space to the exhaust grille. From the grille on, you do the regular pressure drop calculation and add the numbers you mention. but again, whoever gave you those numbers, also should provide information how they came up with it. the space in question sia a large plenun, which is an oversized duct. So you could calculate something and add some safety. huge duct.

If you exhaust from a space, you need make-up air. If that infiltrates through the walls, there is pressure drop. if that comes through a MUA, you add pressure. So you need to look at all the air that leaves AND enters the space.

 

[Yunushumayun]

Our exhaust system has no ducts, roof mounted fans are installed without any ducts, but the client is requesting for static pressure value, we need to prove them that in non ducted system we dont need to calculate external static pressure, need reference document from any standards for exhaust system

 

[GT-EGR]

The reference standard would be the manufacturers stating and testing and standing by the unducted performance of the fan. I guess you could ask them for their testing documentation?

If there is no ductwork, the fan is just free flowing air from atmosphere to atmosphere. All it needs pressure for is to create the velocity pressure of the air which all fans do as part of their internal/packaged performance.

Unless the atmospheric pressures on the two sides of the fans are different, you have nothing external to overcome. It will be hard to find a reference standard spending time on this level of concept - but maybe look for this type where pressure inside and outside of building are slightly different.

 

[nuuvox000]

If you're pulling air from a space with no openings then static pressure would build up very high and very quickly. You need to show that the openings in the building are sufficiently large or sufficient in number that you won't exceed 0.2" external static pressure with the amount of CFM you're exhausting. You can think of it as if the building is a large duct that the fan is attached to; where are the openings to get air into the building? There is a table in ASHRAE HVAC Applications that you can use to estimate the tightness of the building. Page 53.7, table 2 "Typical flow areas of walls and floors of commercial buildings."